(a) Field of the Invention
The present invention relates to a method of producing a naphthol-modified phenolic resin which is excellent in heat resistance and insulating properties and is suitable for use as a molding material resin or a hardener for epoxy resins.
(b) Description of the Related Art
Phenolic resins are classified roughly into novolak phenolic resins and resol phenolic resins, both of which exhibit excellent properties as binders of organic or inorganic base materials.
Recently, the requirement for the properties of phenolic resins has become strict, requiring higher heat resistance, higher strength and lower hygroscopicity. A possible means of improving these properties is introduction of comonomers having a fused ring structure, such as naphthols. However, naphthols have a larger reactivity than phenols, so that conventional catalysts for the synthesis of resol resins or novolak resins, such as acids, metal oxides, metal chlorides, metal hydroxides and amines cannot produce resins of high molecular weight.